As you are new to computers, you probably do the sensible thing and let all programs save their files in the "My Documents" folder (or sub-folders).
If that's the case then you can simply move "My documents" to you D drive.
If you do that, not only will existing documents, pictures etc be moved, but new documents and pictures will automatically be saved there as well.
You can move "My Documents" as follows:
RIGHT-click the "My Documents" icon on the desktop, and choose Properties
Click the Move button
In the window that appears, click the little plus sign to the left of "My Computer"
Click once on your D drive
Click the button at the bottom "Make New Folder"
Call the folder something like PepperMum Docs.
Click OK
You will now see that in the properties window, the Target is "D:\Peppermum Docs
Click OK
When it asks if you wand to move all the documents in the old location to the new location, say Yes (it may take some time)
That's it.